ATT announced starting today the company is offering T-Mobile customers the opportunity to upgrade their mobile with value of up to $450 per line when they switch to ATT and trade in an eligible smartphone. Here are some of the details on this unique offer:

Beginning Jan. 3, under the limited-time offer, T-Mobile customers who switch to AT&T can trade-in their current smartphone for a promotion card of up to $250, which can be used toward AT&T products and services. Trade-in values will vary based on make, model and age of the smartphone, but many of the latest and most popular smartphones will qualify for a value of $250. T-Mobile customers can receive an additional $200 credit per line when they transfer their wireless service to AT&T and choose an AT&T Next plan, buy a device at full retail price or activate a device they currently own.